1. Field of the Invention
In certain embodiments, the invention disclosed herein relates to analogs of peptides corresponding to class I MHC-restricted T cell epitopes and methods for their generation. These analogs can contain amino acid substitutions at residues that directly interact with MHC molecules and can confer improved, modified or useful immunologic properties. In particular, epitope analogs from the tumor-associated antigens SSX-2, NY-ESO-1, PRAME, PSMA, tyrosinase, and melan-A are identified. Additionally, classes of analogs, in which the various substitutions comprise the non-standard residues norleucine and/or norvaline, are disclosed.
2. Description of the Related Art
The Major Histocompatibility Complex and T Cell Target Recognition
T lymphocytes (T cells) are antigen-specific immune cells that function in response to specific antigen signals. B lymphocytes and the antibodies they produce are also antigen-specific entities. However, unlike B lymphocytes, T cells do not respond to antigens in a free or soluble form. For a T cell to respond to an antigen, it requires the antigen to be bound to a presenting complex comprised of major histocompatibility complex (MHC) proteins.
MHC proteins provide the means by which T cells differentiate native or “self” cells from foreign cells. MHC molecules are a category of immune receptors that present potential peptide epitopes to be monitored subsequently by the T cells. There are two types of MHC, class I MHC and class II MHC. CD4+ T cells interact with class II MHC proteins and predominately have a helper phenotype while CD8+ T cells interact with class I MHC proteins and predominately have a cytolytic phenotype, but each of them can also exhibit regulatory, particularly suppressive, function. Both MHC class I and II are transmembrane proteins with a majority of their structure on the external surface of the cell. Additionally, both classes of MHC have a peptide binding cleft on their external portions. It is in this cleft that small fragments of proteins, native or foreign, are bound and presented to the extracellular environment.
Cells called antigen presenting cells (APCs) display antigens to T cells using the MHC. T cells can recognize an antigen, if it is presented on the MHC. This requirement is called MHC restriction. If an antigen is not displayed by a recognizable MHC, the T cell will not recognize and act on the antigen signal. T cells specific for the peptide bound to a recognizable MHC bind to these MHC-peptide complexes and proceed to the next stages of the immune response.